This invention pertains to the art of fluid pumping devices and more particularly to devices including a diaphragm actuated pumping motion.
The invention is particularly applicable to blood pumps useful as a ventricle assist or replacement devices and is intended for use as a human heart pump. However, it will be appreciated to those skilled in the art that the invention could be readily adapted for other uses as, for example, where similar pumping devices are employed in an environment where highly reliable pumping action is required in a location with a minimal amount of space and which must also avoid interference or action upon items or organs adjacent the pump.
Three overall design objectives motivate this configuration of blood pump. They comprise, first, a better fit in the patient; second, more practical insertion and application for a surgeon; and, finally more controlled pumping action.
Most known blood pumps run on pneumatic systems including an elastomeric diaphragm for pumping the blood that is actuated by an external driver. It has been found that a guide for the diaphragm motion is desirable because absent the guide the diaphragm can move erratically in response to the dynamic actuating and blood pressures and cause problems with an irregular blood pumping motion. Such irregular motions may cause local stagnation, consequent clotting and increased diaphragm stresses and may make it difficult to measure the diaphragm movement and therefore calculate flow volume. The guide will be fixed to the diaphragm with a pusher plate and will provide a smooth linear motion of the diaphragm in response to the actuating pressure. The guide may also limit the maximum travel and prevent damage to blood elements or pump components.
Typically, the pusher plate will be guided by a shaft and bearing arrangement The shaft is fixed to the pusher plate which is in turn fixed to the diaphragm and the shaft slides through a bearing in a direction perpendicular to the diaphragm The bearings are fixed in the blood pump housing and the shaft will have a stroke length equal to the actuated movement of the diaphragm.
The particular problem with guide mechanisms of this type is that there is a space requirement within or without the housing equal to the stroke length of the pusher plate shaft. A protrusion in the sidewall of the housing has been employed to accommodate the shaft stroke length when the shaft is in a fill position where the diaphragm is in a disposition to maximize the volume of the blood chamber. When the blood is ejected from the blood chamber and the diaphragm and pusher plate are moved to minimize the volume of the blood chamber, the shaft will be drawn out of the protrusion and into the pump housing.
Although such pump constructions can satisfactorily guide the diaphragm movement, they fail to satisfy all the above cited overall design objectives. The protrusion does not provide a better fit in the patient and insertion of such a cumbersome blood pump in the patient can cause substantial problems for the surgeon. In particular, it has been found that a design having a protrusion in the sidewall will necessitate cutting away some of the rib and adjacent tissue in the patient to accommodate the protrusion when the pump is placed up against the rib cage. When the pump is in the abdomen, the actuator projection places unnecessary and potentially damaging pressure on surrounding organs. Such surgical necessities impose a substantial reluctance against the use of blood pumps of this design.
The present invention contemplates a new and improved pump which overcomes the problems discussed above and others to provide a new pump useful as a ventricle assist or replacement device which provides improved control of pumping action, is simple in design, readily adaptable to a variety of dimensional characteristics, easy to implant, operate and remove, and which provides a better fit in the patient, and practical insertion and application for the surgeon.